I personally had two sets of "custom" engineered springs from Alcan fail. Set one went completely flat within 100 miles of home and ruined a Moab trip. Set 2 dropped 4" of height within 1000 miles and put a serious strain on an Alaskan trip. Not to mention the 4 ruined tires. If you have a heavy 60 series I would look at OME only, period ..... been there done that already. Bob
I 3rd that and also would like to know how you lost 4" of height unless you were running a huge SUA lift, which woudl cause issues as well.
As with every post when I reccoment Alcans just get them to make the springs a little longer to help with the shackle angles.